Welcome to the forums, Guilherme.
Let's slow down a bit here; there's too much to deal with all at once.
- Why do you assume we are all 'fellows'?
- Has anybody ever told you that proper nouns like Brazilian and the personal pronoun I are always capitalised?
- What's 'Wizard'?
- How old are your students?
- You have already used 'at' correctly. Why don't you try to use 'in' and 'on' in sentences of your own?